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An exposure characterization of a large scale application of a biological insecticide, Bacillus thuringiensis.

The characterization and documentation of exposure potential to Bacillus-thuringiensis (Bt), a biological insecticide used to eradicate the gypsy-moth, was presented. Bt was chosen for use in the state of Oregon for treatment of approximately 250,000 acres of forested and urban areas in Lane County in 1985 and 1986; personal exposure and area monitoring for Bt was conducted to determine occupational and nonoccupational exposure potential. Portable sampling pumps with membrane filters were used for air sampling; microbial culture techniques were used to identify Bt by toxin crystal formation. Occupational exposure ranged from 0 to 5600 colony forming units of Bt per cubic meter (CFU/m3); general public Bt exposure ranged from 0 to 1600CFU/m3. The results of the survey demonstrated ubiquitous distribution of Bt after application. The 1985 sampling method was not entirely adequate for quantitative determination of Bt environmental levels; improvements to the procedure in 1986 involved increasing the sampling flow rate and duration, using additional precautions to reduce contamination as a result of aseptic technique during the preparation and handling of blanks, and determining if indigenous strains of Bt were present (they were not). The authors conclude that while the gypsy-moth eradication project was extremely effective, Bt application of the magnitude used temporarily promotes widespread distribution of the organism throughout the environment.